fix: prevent asset conflicts between React and Grid.js versions

Add coexistence checks to all enqueue methods to prevent loading
both React and Grid.js assets simultaneously.

Changes:
- ReactAdmin.php: Only enqueue React assets when ?react=1
- Init.php: Skip Grid.js when React active on admin pages
- Form.php, Coupon.php, Access.php: Restore classic assets when ?react=0
- Customer.php, Product.php, License.php: Add coexistence checks

Now the toggle between Classic and React versions works correctly.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

node_modules/autoprefixer/lib/hacks/mask-border.js

@@ -0,0 +1,38 @@
+let Declaration = require('../declaration')
+
+class MaskBorder extends Declaration {
+  /**
+   * Return property name by final spec
+   */
+  normalize() {
+    return this.name.replace('box-image', 'border')
+  }
+
+  /**
+   * Return flex property for 2012 spec
+   */
+  prefixed(prop, prefix) {
+    let result = super.prefixed(prop, prefix)
+    if (prefix === '-webkit-') {
+      result = result.replace('border', 'box-image')
+    }
+    return result
+  }
+}
+
+MaskBorder.names = [
+  'mask-border',
+  'mask-border-source',
+  'mask-border-slice',
+  'mask-border-width',
+  'mask-border-outset',
+  'mask-border-repeat',
+  'mask-box-image',
+  'mask-box-image-source',
+  'mask-box-image-slice',
+  'mask-box-image-width',
+  'mask-box-image-outset',
+  'mask-box-image-repeat'
+]
+
+module.exports = MaskBorder